Turbine blade construction



July 28, 1970 F. ZERLAUTH 3,521,974

TURBINE BLADE CONSTRUCTION Filed Sept. 11. 1968 Inventor- Ferdinand Zerlourh BY @M' ,J

ATTORNEYS United States Patent O1 Ffice US. Cl. 416220 7 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a turbine blade whose root includes a cylindrical portion and a plurality of spaced plane surfaces against one or another of which a suitably selected clamping ring can be brought to bear in order to detune the natural frequency of oscillation of the blade from oscillation frequencies to be encountered by the blade in service.

The present invention pertains to a blade construction for turbomachines, e.g. a stator blade construction for turbo-compressors. The term turbomachine is intended to denote a turbine-type machine whether for development of mechanical energy at a rotating shaft from a fluid flowing through the machine as in a turbine, or for the delivery of energy from a rotating shaft to the fluid, as in a pump or compressor. In accordance with the invention the foot or root of the blade includes at least one circularly cylindrical surface and at least two plane surfaces perpendicular to the axis of that cylindrical surface. It also includes a thread so that, in accordance with the vibrational conditions obtaining, the blade may be fastened into the cylindrical bore of a blade carrier with the help of a nut engaged on the thread, with the help of a clamping ring bearing against the cylindrical surface and against one of the plane surfaces, and with the help of a wedging ring having a conical bore which is drawn down over the first-named ring.

By means of the construction of the invention the blade can be detuned from the frequency of oscillations existing in the vicinity thereof, for example those in the fioW of the working substance, so that the blade will not be set into corresponding sympathetic vibrations. Consequently, no resonance builds up and there is no critical range of oscillations. In addition, the blade can be easily set to the desired angle or pitch and if necessary can be easily corrected in that respect.

The root of the blade can be provided with an annular neck or constriction with the help of which large changes in the natural period of vibration of the blade can be achieved in the initial manufacture thereof. The fine adjustment in this respect is made on assembly by suitable choice in the positioning of the clamping ring applied to one or another of the plane surfaces.

To check proper application of the clamping ring against one or the other of the plane surfaces it is advantageous to provide a bore in the blade carrier. The clamping ring can then be split into two or more parts and the wedging ring can be similarly split.

BRIEF DESCRIPTION OF THE DRAWING The invention will now be further described in terms of a non-limitative presently preferred exemplary embodiment thereof and with respect to the accompanying drawings, in which:

FIG. 1 shows in simplified form a blade construction according to the invention having a clamping ring bearing against one of two plane surfaces; and

3,521,974. Patented July 28, 1970 FIG. 2 is a similar view showing a clamping ring hearing against the other of those plane surfaces.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the blade 12 possesses a root portion 11 with the help of which the blade is to be fastened in a blade carrier 23. The carrier 23 possesses a shape matching the groove in a rotor or stator blade ring so that in customary fashion it can be set thereinto. With additional necessary blades the result is one stage of rotor or stator blading of a turbomachine such as a steam turbine, gas turbine or axial compressor, for example.

As shown in the drawing the root 11 of the blade 12 may be shaped as a body of revolution, for example by a turning operation or operations. The blade root possesses a circularly cylindrical surface 13 and two plane surfaces 16 and 17, perpendicular to the axis of the surface 13. In addition the root includes a thread 18, onto which a nut 24 can be run. According to the frequency of the oscillations to which the blade is exposed in use a clamping ring 19.1 can be brought, as in FIG. 1, to bear against the circularly cylindrical surface 13 and against the plane surface 16. Alternatively, as in FIG. 2, a clamping ring 19.2 can be brought to bear against the surface 13 and against the plane surface 17. The clamping rings 19a and 19b possess a conical outer surface 20. This conical surface mates with the conical bore of a covering or wedging ring 21. When the ring 21 is drawn down against the clamping ring 19a or 19b by means of nut 24, the two rings will be wedged against each other and between the cylindrical surfaces 13 and 22, so that the root 11 and blade 12 will be locked both axially and angularly with respect to the blade carrier 23.

During tightening of the nut 24, the blade and blade support can be held in the proper relative position by means of jigs, which canbe inserted for example into the groove 28 to bear against the root and against the profile of the blade. The result will be that after tightening of the nut has been completed, the blade will be correctly positioned.

The bores 26 in the blade carrier 23 serve to permit subsequent observation as to which of the clamping members 19a and 19b has been employed in the completely assembled blade. The blade carrier 23 (of which there may be a plurality in any one blade ring) can have any desired profile to be set into circular closed blade grooves or in transverse grooves of plates or other blade-supporting elements.

For rough matching of the blades to the vibration conditions thereof a groove 25 or constriction can be provided in the root 11. By means of these grooves 21 desired preliminary detuning can be achieved for the blade with respect to the vibration frequency expected to be encountered. By selection of the appropriate one of the clamping members 19a and 19b, the frequency can be further brought to the desired value without mechanical attack upon the blade.

The invention thus provides a turbine blade construction which facilitates accurate and secure positioning of the blades, and which also permits, by choice among rings such as the rings 19a and 19b in the embodiment de scribed, change in the free unsupported length of the blades. This permits control of their natural frequency of vibration, so as to detune them from oscillations to which they may be exposed in service.

While the invention has been described hereinabove in terms of a presently preferred embodiment thereof, the invention itself is not limited thereto but rather comprehends all modifications of and departures from that embodiment properly falling within the spirit and scope of the appended claims.

I claim: v

1. A turbine blade construction comprising:

(a) a blade carrier having a cylindrical bore therein,

(b) a blade having a root affixed thereto,

(0) the root having formed thereon (l) a circularly cylindrical surface, (2) at least two spaced plane surfaces transverse of the axis of the cylindrical surface, and (3) a thread, said construction further comprising:

(d) a clamping ring having a conical outer surface,

(e) a wedging ring having a conical inner surface, and

(f) a nut, said clamping ring being engageable with said cylindrical surface and with one of said plane surfaces whereby upon tightening of said nut said rings will be wedged against each other between said cylindrical surface and cylindrical bore.

2. A blade construction according to claim 1 wherein said blade is shaped with a constriction adjacent the root thereof.

3. A blade construction according to claim 1 wherein said blade carrier has an opening formed therein adjacent one of said plane surfaces.

4. A blade construction according to claim 1 wherein said wedging ring is split.

5. A blade construction according to claim 1 wherein said wedging ring comprises a plurality of sectors.

6. A blade construction according to claim 1 wherein said clamping ring is split.

7. A blade construction according to claim 1 wherein said clamping ring comprises a plurality of sectors;

References Cited UNITED STATES PATENTS 2,955,799 10/1960 Oickle.

FOREIGN PATENTS 141,466 6/ 1951 Australia. 724,793 9/ 1942 Germany.

EVERETTE A. POWELL, JR., Primary Examiner US. Cl. X.R. 416-500 

